1 package (14.4 ounces) frozen pearl onions, thawed and drained
2 cups heavy whipping cream
1/2 cup grated Parmesan cheese
1/2 teaspoon salt
1/4 teaspoon pepper
10 ounces fresh baby spinach (about 13 cups)
In a large cast-iron or other heavy skillet, heat butter over medium heat. Add pearl onions; cook and stir until tender, 6-8 minutes. Stir in cream. Bring to a boil; cook until liquid is reduced by half, 6-8 minutes.
Stir in cheese, salt and pepper. Add spinach; cook, covered, until spinach is wilted, 3-5 minutes, stirring occasionally.